New York police arrested one man with a fake U.S. pilot's license and detained at least five others Thursday evening as federal officials, fearing another wave of terrorist attacks against Americans, intensified an international manhunt designed to track down a ring of suspects responsible for the deadliest terrorist attack in U.S. history.

Justice Department officials said they have identified all 18 hijackers of the four planes used in the attacks on the World Trade Center and the Pentagon and on the plane that crashed in a Pennsylvania field. Meanwhile, police and federal agents portrayed those who planned the attacks as members of a wide-ranging global conspiracy involving more than one terrorist group.

New York Police Commissioner Bernard Kerik revealed the arrest and detentions at John F. Kennedy and at La Guardia Airports. Kerik said the suspects may have had fictitious IDs and possessed knives and had open airline tickets for the morning of Sept. 11 departing Kennedy and La Guardia Airports. "One was arrested with identification indicating he was a pilot." Kerik said. "He tried to clear security. He was stopped. The identification he had was false. He has been arrested."

After the arrest, the New York region's three major airports--Kennedy, La Guardia and Newark, N.J.--opened briefly and then abruptly closed late Thursday afternoon.

The arrests, and the suggestion that there remain active cells of terrorists at large, came as investigators broadened their investigation, sweeping into Germany and Canada.

U. S. Atty. Gen. John Ashcroft said the two planes that hit the World Trade Center were overtaken by five hijackers each while those that slammed into the Pentagon and crashed outside Pittsburgh were seized by four individuals each.

The portrait of the suspects that emerged Thursday showed they had integrated themselves into the normal byways of American life to a remarkable degree without having to retreat underground. They lived in attractive U.S. suburbs, trained in American flight schools and drank at local bars.

U.S. officials also said for the first time that several groups may have been involved in the attacks, contrasting with earlier statements that focused more directly on Osama bin Laden as the principal mastermind and suggesting a broader, more complex conspiracy years in the making.

"They are increasingly confident that bin Laden is involved," Rep. Henry Hyde (R-Ill.), chairman of the House International Relations Committee, said after a briefing by intelligence officials. "But the CIA pointed out they are increasingly convinced that there are other terrorist networks involved, that there is a vast linkage of networks."

A senior Bush administration official confirmed "there might have been not just one, but multiple organizations."

Ashcroft said the number of known associates of the terrorists in the United States was "significant" and increasing as the investigation continued. A Justice Department official, speaking on condition of anonymity, said there were "probably more than 30 associates" operating in groups within several cities. Some may have already fled the country.

The Justice Department announced it would release the names of all 18 hijackers Thursday evening, along with their photos. But officials delayed the announcement, then dropped it entirely without explanation.

The names of seven of the hijackers emerged Thursday, nonetheless, providing a glimpse into the lives of the men who took over the planes, slashed and killed many of the flight attendants and set the airliners on suicide flight paths into the World Trade Center and the Pentagon.

Several were Saudi Arabian nationals or worked for Saudia, the Saudi Arabian national airline. Two of the hijackers were cousins, and at least four lived in Florida for a time and received pilot training there.

Mohamed Atta, Waleed Alshehri, Wail Alshehri, Abdulrahman or Abdulaziz Alomari, and Satam Al Suqami were the five hijackers who took over American Airlines flight 11, en route from Boston to Los Angeles, and slammed it into the World Trade Center, setting off the day's nightmare, according to a source familiar with the FBI's list of the hijackers.

Marwan Alshehri, 23, was aboard United Airlines Flight 175, the second craft to hit the World Trade Center, according to German officials.

Hanish Hanjour, 26, who lived in Oakland, Calif., was one of the hijackers on American Airlines Flight 77, which took off from Dulles International Airport outside Washington and smashed into the Pentagon.

A Chinese news service reported in 1987 that a Palestinian named Mohamed Atta had been arrested in New York because he was wanted by Israeli authorities for murdering a bus driver in Israel. It was not clear whether it was the same individual.

Atta and Alshehri received pilot training in several Florida flight academies, including Huffman Aviation International in Venice, and FBI agents have descended on the school. Azzan Ali, 20, a native of Oman who is a student at the flight school, said he was interviewed by three agents Wednesday.

The two were roommates and owned a maroon Pontiac Grand Prix, Ali said, apparently the same car found by authorities at Boston's Logan Airport after the terrorist attacks.

"They never mentioned anything against Americans," Ali said. "They didn't talk bad about the United States."

Ali said the two once flew him to Boca Raton on a flying exercise.

Atta and Alshehri also took two sessions at a flight simulation center called SimCenter, at Opa-locka Airport near Miami, last December, according to Brian George, who helps his father run the facility.

The sessions, simulating flight in a Boeing 727, were part of an introductory course in jet training, which allows a person who has a commercial license to "transition" into jet aircraft.

"It kind of gives you a feel of what it's like to get behind the wheel of a big one," George said.

The 727 is a three-engine jet with an old analogue cockpit, while the 767s that rammed the World Trade Center have modern glass cockpits with video screens, digital airspeed readouts and other sophisticated equipment.

SimCenter owner Henry George told the FBI on Wednesday that Atta and Alshehri said they were from Egypt.

Smith said Atta spoke English well and paid in cash. She called the FBI on Wednesday morning after hearing that one of the suspects had lived in Hollywood, Fla., and recalling that Atta had given an address in that city.

The FBI's pursuit of Atta and Alshehri took them to Hamburg, Germany, where the two lived for an unspecified time. On Wednesday, German authorities forcefully entered an apartment the two had occupied, a German official said.

The two were studying electrical engineering in Harburg, a suburb of Hamburg. "They had visas for being in Germany and everything was legal," the official said.

Authorities also took an airport employee into custody and were searching for another individual in connection with Tuesday's attacks.

Three of the hijackers belonged to a terror group formed "with the aim of carrying out serious crimes together with other Islamic fundamentalist groups abroad, to attack the United States in a spectacular way through the destruction of symbolic buildings," Kay Nehm, Germany's top prosecutor, told reporters.

Details also emerged about Alshehri, who like Atta was aboard American Airlines Flight 11. For a few months in 1999, Alshehri lived in a makeshift boarding house on a quiet street in Vienna, Va. Hamid Keshavarznia, who owns the house, said he's "99 percent sure" the short-term tenant he remembers is Alshehri.

Keshavarznia said he knew very little about the young-looking, quiet man who rented one of the house's six rooms. Alshehri stayed less than six months, Keshavarznia said.

"I don't think he had a job," Keshavarznia said. "He said he was studying, but he never told me what."

Alshehri explained his departure by saying he was headed home to Saudi Arabia to visit his father, then to England to pursue a master's degree, his landlord said.

Why Alshehri was living in a boarding house in a blue-collar neighborhood in the leafy northern Virginia suburb--which is about 12 miles from Washington--is unclear.

Keshavarznia said he believed Alshehri was living on checks from his father, whom Alshehri had described as a businessman and diplomat. "He looked too innocent to be suspicious," Keshavarznia said. "Nice guy, clean cut."

It is not clear where Alshehri went after he left the Virginia boarding house. But before then, Alshehri lived in Daytona Beach, Fla., and received pilot training in Florida, like many of the other possible hijackers. The FBI has been looking at records in the Daytona Beach apartment.

FBI agents also have been scouring Embry-Riddle Aeronautical University, a prominent flight school with a Daytona Beach campus. Two sources at Embry-Riddle confirmed that Alshehri graduated in 1997 and that the FBI has been looking into his past.

Agents arrived at the school shortly after the hijackings, one of the sources said, and began matching names from passenger lists with the school's enrollment records. Several of the names matched, he added, and agents are trying to confirm that the passengers and the students are the same people.

The investigation came as students received another, perhaps more disturbing piece of news. Another Embry-Riddle gradate, David Charlesbois, was the first officer on American Airlines Flight 77, which crashed into the Pentagon on Tuesday.

The investigation, with more than 7,000 FBI personnel and investigators from other agencies, began spreading around the world, Ashcroft said.

In France, anti-terrorism prosecutors tried to find links between the suspects here and militant Islamic networks in their country, while police in Rome reopened the case of a theft of uniforms and badges belonging to two American Airlines pilots in April.

The Royal Canadian Mounted Police in Halifax, Nova Scotia, were helping the FBI follow leads that suggested that some of the hijackers entered the U.S. through Canada, according to Sgt. Wayne Noonan. Investigators were focusing on the ferry service between Yarmouth, Nova Scotia, and Portland, Maine. In addition, police in Halifax confiscated a rented blue Chevrolet Malibu that was found at that city's international airport.

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